Linear electromechanical actuators can be bonded to substrates to control vibration, to position elements, to control noise and for many other functions. Normally, in vibration control applications, a linear actuator is bonded to a substrate and is cycled out of phase to counteract the vibrations induced in the substrate by an external force. During cycling with an alternating voltage, the actuator expands or contracts when voltage is at the peak of a cycle and contracts or expands when voltage is inverted to produce the desired stress which is transmitted to the substrate. In response to such an electric field, an actuator is capable of producing linear displacement of, for instance, about 10 microns in 10 microseconds. With one expansion and one contraction constituting one cycle, a typical linear piezoelectric actuator bonded to a substrate with a reliable epoxy adhesive is capable of undergoing about 10.sup.4 to 10.sup.5 cycles before failure.
The present practice in externally bonded linear actuators produces stress distributions that feature high stress concentrations at the opposite ends of the actuator and in the actuator-substrate bond. The stresses at the interface ends are the main source of actuator authority on the substrate. The stress concentrations that arise at the interface ends accelerate mechanical degradation, fatigue, debonding and fracture of the interface between the actuator and the substrate to which the actuator is bonded. Mechanical degradation, fatigue, debonding and fracture lead to loss of actuator authority, a shortened life of the bond between the actuator and the substrate, and failure of the structure comprising the actuator and substrate to operate as designed. Failure can occur in the bond or in the actuator.
Piezoelectric actuators of the type noted herein are typically rectangular and commonly have dimensions of about 1-4 cm by 1-4 cm with a thickness of about 0.01-0.5 cm.